David Jewitt and Jane Luu detected a small, icy planetesimal - some 155 miles across - out beyond the orbit of Pluto, the most distant of all the planets.
The object is known in astronomical parlance as 1993FW. But Drs Jewitt and Luu have given it a far more romantic designation than the prosaic nomenclature of science.
When not observing the heavenly bodies, they while away the night hours reading the novels of John Le Carre; and, as they had already christened their first discovery 'George Smiley' it seemed only natural that they should have named their second find after his great opponent 'Karla'.
In keeping with the fictional Karla's mysterious movements, the astronomers have captured only a faint, fuzzy image of the planetesimal. But their picture is the reflection of sunlight that has made a round trip of about 7.8 billion miles out to Karla and then back again to enter their telescope.
Smiley and Karla are the first constituents to be detected from the Kuiper belt - this time named after Gerrit Pieter Kuiper, a Dutch astronomer, rather than a fictional hero - which contains small, icy objects left over from the formation of the solar system. Astronomers have long believed that the Kuiper belt had to exist - theory demanded it - but like so many of George Smiley's opponents, it has proved rather hard to track down.
Drs Luu and Jewitt discovered the objects using the 88in telescope belonging to the Institute for Astronomy at Honolulu, Hawaii. Dr Jewitt is an expatriate Englishman, who has been working at the University of Hawaii for years.
The telescope is located near the summit of the extinct volcano, Mauna Kea.
The two astronomers have been searching for members of the Kuiper belt for many years, but they have been helped by recent developments in detector technology - astronomers never actually look through their telescopes any more, they take photographs, attach instruments, or even put highly sophisticated versions of TV cameras, known as charge-coupled devices, on to the business end of the telescope.
According to Dr John Davies, of the Royal Observatory Edinburgh, 'it is an important discovery. Within the past few years, a lot of interesting things have been found in the solar system.' Last year, a different group found a similar object not far from the orbit of Saturn: 'I was the first person to get an infra- red spectrum on it and it was really unusual - most probably covered in organic molecules.
'These planetesimals are the builders' rubble left over from the formation of the solar system and now we have found some we have the hope of finding out what they are made from,' he added.